For simplicity I want to keep damage to doubles out of the class. Doubles just have 1 hit point when within the conduits dimension and return uninjured and unhampered to their own dimension no matter what happens to them (even death). The conduit sustains any overflowing damage.

Don’t forget that a double is only ever in play during your action. The conduit is in play the rest of the time. So the majority of a foes attacks target the Conduit, not her doubles. Doubles do get bonuses to saves and to their AC against AOO as well, so they are bolstered defensively against attacks and effects which target them whilst they are in play.

Additionally a double who sustains damage instantly returns to their home dimension, so any powers or abilities which allow a double to sustain damage in order to produce an effect are essentially fruitless (the double vanishes from the conduits dimension before they can be completed).

If any aspect of the above is unclear I will try to make its more transparent.

The core thing I want to achieve is simplicity in this regard. I don’t want players to have to worry about things ticking over on their doubles while they are not in play. Over complexity and full administration of 6+ character sheets is to be avoided. This is why doubles can essentially be written as though they wear the conduits armour and hold his items (though this also helps balance out the class and removes access to the doubles own personal wealth of items housed in their home dimension).

I want things to be fluid once in play. BAM I’m using my wizard then next turn BAM I’m using my monk.